Method and apparatus for facilitating fault tolerance in a radio frequency amplifier system

ABSTRACT

N input signals are fed ( 702 ) to a first Fourier Transform Matrix (FTM) ( 208 ) to produce N intermediate signals. Each of the N intermediate signals is split ( 704 ) via a non-isolating splitter ( 300 ) to produce M split signals. At least one of the M split signals from each of the N intermediate signals is amplified ( 706 ) to produce at least N amplified signals. The at least N amplified signals are coupled ( 708 ) to N non-isolating combiners ( 300 ), each having at least M input ports, to produce N combiner output signals. The N combiner output signals are applied ( 710 ) to a second FTM ( 210 ) to produce N final output signals.

FIELD OF THE INVENTION

This invention relates in general to radio frequency (RF) communicationsystems, and more specifically to a method and apparatus forfacilitating fault tolerance in a radio frequency amplifier system.

BACKGROUND OF THE INVENTION

It is well known that a Fourier Transform Matrix (FTM) can be used in amulti-carrier RF communication system for distributing a plurality of RFsignals among multiple amplified paths, and for recovering the pluralityof RF signals after amplification. Advantages associated with using theFTM include a reduced peak-to-average power requirement for theamplifiers, greater efficiency of amplifier utilization, and a degree ofredundancy.

Unfortunately, the redundancy provided by the prior-art FTM technique isnot perfect. When a failure occurs in one of the amplified paths, theinsertion loss encountered by each of the RF signals is degraded, andthe isolation between the RF signals is also degraded. For example, in a4×4 FTM, if a singular amplified path is disrupted, insertion loss foreach RF signal will degrade by approximately 2.5 dB, and the isolationbetween the RF signals will be reduced substantially—in some cases by 30to 40 dB.

Thus, what is needed is a method and apparatus for facilitating faulttolerance in an RF amplifier system. The method and apparatus preferablywill tolerate a failure in one of the amplified paths with minimaldegradation of insertion loss and without producing a substantialreduction in isolation between the RF signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages inaccordance with the present invention.

FIG. 1 is one form of an electrical circuit of a prior-art FourierTransform Matrix (FTM).

FIG. 2 is an electrical block diagram of a prior-art 4×4 FTM amplifiernetwork.

FIG. 3 is one form of an electrical circuit of a prior-art non-isolatingsplitter/combiner.

FIG. 4 is an electrical block diagram of an exemplary 4×4 FTM amplifiernetwork in accordance with the present invention.

FIG. 5 is a simplified electrical block diagram of an exemplaryamplifier switching arrangement in accordance with the presentinvention.

FIG. 6 is an electrical block diagram of an exemplary fault-toleranttransmitter in accordance with the present invention.

FIG. 7 is a flow diagram depicting a method for facilitating faulttolerance in an RF amplifier system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In overview, the present disclosure concerns radio frequency (RF)communication systems. More particularly, various inventive concepts andprinciples embodied as a method and apparatus for facilitating faulttolerance in an RF amplifier system for use in equipment with such RFcommunications systems will be discussed and disclosed. The RFcommunications systems of particular interest are those being deployedand developed such as Integrated Dispatch Enhanced Networks fromMotorola, Inc. and cellular systems and evolutions thereof that utilizemulti-carrier amplifiers, although the concepts and principles haveapplication in other systems and devices.

The instant disclosure is provided to further explain in an enablingfashion the best modes of making and using various embodiments inaccordance with the present invention. The disclosure is further offeredto enhance an understanding and appreciation for the inventiveprinciples and advantages thereof, rather than to limit in any mannerthe invention. The invention is defined solely by the appended claimsincluding any amendments made during the pendency of this applicationand all equivalents of those claims as issued.

It is further understood that the use of relational terms, if any, suchas first and second, top and bottom, and the like are used solely todistinguish one from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. Much of the inventive functionality and many of theinventive principles are best implemented with or in one or moreconventional micro-strip circuits, or with conventional microprocessors.It is expected that one of ordinary skill, notwithstanding possiblysignificant effort and many design choices motivated by, for example,available time, current technology, and economic considerations, whenguided by the concepts and principles disclosed herein will be readilycapable of programming such microprocessors, or generating suchmicro-strip circuits with minimal experimentation. Therefore, in theinterest of brevity and minimization of any risk of obscuring theprinciples and concepts according to the present invention, furtherdiscussion of such microprocessors and micro-strip circuits, if any,will be limited to the essentials with respect to the principles andconcepts employed by the preferred embodiments.

Referring to FIG. 1, one form of an electrical circuit of a prior-artbasic 2×2 Fourier Transform Matrix (FTM) 100 includes first and secondinputs 102, 104 coupled to a plurality of tees 110 and quarter-wavetransmission lines 112, arranged as depicted, and having first andsecond outputs 106, 108. The basic 2×2 FTM 100 is also sometimesreferred to as a branch line coupler. It will be appreciated that,alternatively, other forms of FTM circuits can be utilized to producequadrature signals at the first and second outputs 106, 108. RFamplifier networks comprising FTMs are well-known and have exhibited theadvantages and problems discussed briefly in the Background. For furtherinformation on the application of FTMs to RF amplifier networks, thereader is referred to “4×4 Hybrid Matrix Power Amplifier” by JeffMerrill, published October 1998 in Wireless Design and Development.

Referring to FIG. 2, an electrical block diagram of a prior-art 4×4 FTMamplifier network 200 includes a first 4×4 FTM 208 comprising four ofthe basic FTMs 100 coupled as shown. The first 4×4 FTM 208 includes fourFTM inputs 204 for receiving four separate input signals, and furtherincludes four FTM outputs 212-218 producing four intermediate signals.The four FTM outputs 212-218 are coupled, respectively, to fouramplifiers 202, whose outputs are coupled, respectively, to fourcorresponding FTM inputs 220-226 of a second 4×4 FTM 210 comprisinganother four of the basic FTMs 100 coupled as shown to reproduce thefour separate (amplified) input signals at four FTM outputs 206. It ispreferred that the four amplifiers 202 have substantially identicalinsertion phase and gain with respect to one another.

In operation, the first FTM 208 produces the four intermediate signalscomprising phase-shifted mixes of the four input signals at the FTMoutputs 212-218, while the second FTM 210 converts the fourphase-shifted mixes back into the four separate amplified input signals.The amplifiers 202 each amplify one of the four phase-shifted mixes ofthe four input signals. If one of the amplifiers 202 fails, the fourseparate amplified input signals will still appear at the FTM outputs206, but, disadvantageously, with increased insertion loss and reducedisolation between the four signals.

Referring to FIG. 3, one form of an electrical circuit of anon-isolating splitter/combiner 300 comprises a “combined” input/outputnode 302 coupled to the midpoint 310 of a tee 312. A first side 314 ofthe tee 312 is coupled to a first end of a first quarter-wavetransmission line 318. The second end of the first quarter-wavetransmission line 318 is coupled to a first end of a second quarter-wavetransmission line 320, which is used as a phasing line for reasonsdescribed further below. The second end of the second transmission line320 is coupled to a first “split” input/output node 304. A second side316 of the tee 312 is coupled to a first end of a third quarter-wavetransmission line 322. The second end of the third quarter-wavetransmission line 322 is coupled to a first end of a fourth quarter-wavetransmission line 324, which is also used as a phasing line. The secondend of the fourth quarter-wave transmission line 324 is coupled to asecond “split” input/output node 306. It will be appreciated that,alternatively, the first and second quarter-wave transmission lines 318,320 can be replaced by a single half-wave transmission line, as can thethird and fourth quarter-wave transmission lines 322, 324.

An advantage of having one-half wave length of phasing line on each sideof the tee 312 is that when a switch coupling an amplifier to one sideof the tee 312 is opened, e.g., in response to a failure of theamplifier, the resultant open circuit is reflected back to the tee 312,thereby sending the signals that would have gone to the failed amplifierto a remaining operating amplifier instead. One of ordinary skill in theart will recognize that a transmission line of any even multiple ofquarter-wave lengths will produce a similar result. It will beappreciated that, alternatively, a transmission line of any odd multipleof quarter-wave lengths will work as well, if a short circuit ispresented by the switch instead of an open circuit after the switch hasremoved the failed amplifier. It will also be appreciated that thequarter-wave multiples need not be exact, but can be off by a fewpercent without serious consequences.

The splitter/combiner 300 can be utilized as either a splitter or acombiner, depending on the use of the input/output nodes 302-306. Whenthe “combined” input/output node 302 is used as an input, thesplitter/combiner 300 functions as a splitter, producing similar signalsat reduced power at the first and second “split” output nodes 304, 306.When the first and second “split” input/output nodes 304, 306 are usedas inputs, the splitter/combiner 300 functions as a combiner, producinga sum of the input signals at the “combined” output node 302. Forsimplification purposes herein below, the splitter/combiner 300 will bereferred to as either “the splitter 300” or “the combiner 300,”depending upon its application in the portion of the circuit beingdescribed. It will be appreciated that, while the splitter/combiner 300is a two-way splitter/combiner, an M-way splitter/combiner can beutilized as well in accordance with the present invention, where M is aninteger greater than 1.

Referring to FIG. 4, an electrical block diagram of an exemplary andinventive 4×4 FTM amplifier network 400 comprises the first and second4×4 FTMs 208, 210, as utilized in the prior-art network 200. In thenetwork 400, four of the splitters 300 are coupled to the four outputs212-218 of the first FTM 208 for splitting each of the four intermediatesignals of the four outputs 212-218 to produce two split signals fromeach of the intermediate signals. The two split signals are coupled totwo amplifiers 402, 404, arranged with controllable switches in someembodiments such that the amplifiers 402, 404 can be coupled anduncoupled from the network 400 by a controller 602 (FIG. 6), asdescribed further herein below. The outputs of the two amplifiers 402,404 produce two amplified signals corresponding to each of the fourintermediate signals. The two amplified signals corresponding to each ofthe four intermediate signals are coupled to first and second splitinputs of four of the combiners 300 to produce four combiner outputsignals. The four combiner output signals are coupled to the four inputs220-226 of the second FTM 210 to produce four final output signals atthe outputs 206 of the second FTM 210.

An advantage of the network 400 over the prior-art network 200 is thatin the network 400 either of the two amplifiers 402, 404 in the pathscorresponding to the four intermediate signals at the outputs 212-218can be removed from the network 400 without degrading the insertion lossand without significantly reducing the isolation between the four inputsignals being amplified. In fact, either one of the pairs of amplifiers402, 404 corresponding to the four intermediate signals can be removedfrom all four paths corresponding to the four intermediate signals withminimal degradation of the insertion loss and without significantlyreducing the isolation between the four input signals being amplified.This is true, because when one of the amplifiers 402, 404 is removed,the open circuit presented to the tee 312 of the splitter 300 throughthe two quarter-wave phasing lines 318, 320 or 322, 324 reflects thesignal power that would have gone to the removed amplifier back to thetee 312, where it is sent to the remaining amplifier 402, 404 servingthe same intermediate signal path. The output signals are essentiallyunaffected, provided that the remaining amplifier is able to handle theincreased power.

In one embodiment, both of the split signals are amplified to producetwo amplified signals corresponding to each of the four intermediatesignals. The two amplified signals are then coupled to a correspondingone of the four combiners 300 to produce the four combiner outputsignals. In this embodiment, a failure of either amplifier 402, 404 in agiven intermediate signal path will not degrade the output signals,provided that the remaining amplifier 402, 404 can handle the extrapower.

In a second embodiment, both of the split signals corresponding to thefour intermediate signals are amplified when traffic through theamplifier network 400 is above a predetermined threshold. Thepredetermined threshold can be determined, for example, from the maximumpower handling capacity of one of the amplifiers. When traffic is belowthe predetermined threshold, only one of the two split signalscorresponding to each of the four intermediate signals is amplified.This advantageously allows the amplifier network 400 to consume lesspower when traffic is low.

In the second embodiment, when amplifying only one of the two splitsignals corresponding to each of the four intermediate signals, and inresponse to detecting a failed amplifier, the controller 602 and thenetwork 400 are preferably arranged and programmed to uncouple thefailed amplifier and couple a stand-by amplifier to one of the two splitsignals not amplified prior to detecting the failed amplifier. In thisway the failed amplifier advantageously can be replaced seamlessly withno disruption of service.

It will be appreciated that, while the exemplary amplifier network 400has four inputs 204 for receiving four input signals and four outputs206 for producing four final output signals, in the general case theamplifier network in accordance with the present invention can have Ninputs and N final outputs, where N is a first integer greater than one.It will be further appreciated that, while the exemplary non-isolatingsplitter/combiner 300 is a two-way splitter/combiner, in the generalcase the splitter/combiner can be an M-way splitter/combiner and canproduce and combine M split signals, where M is a second integer greaterthan one.

Referring to FIG. 5, a simplified electrical block diagram of anexemplary and inventive amplifier switching arrangement 500 comprises afirst basic 2×2 FTM 100 having two inputs 502 and two outputs 506, 508carrying first and second intermediate signals, respectively. Theswitching arrangement 500 further comprises first and second splitters300 coupled, respectively, to the first and second outputs 506, 508. Thefirst splitter 300 comprises first and second split outputs 530, 532.The second splitter 300 comprises third and fourth split outputs 534,536. The switching arrangement 500 further comprises first and secondcombiners 300. The first combiner 300 comprises first and second splitinputs 538, 540 and a combined output 510 coupled to a first input of asecond basic 2×2 FTM 100. The second combiner 300 comprises third andfourth split inputs 542, 544 and a combined output 512 coupled to asecond input of the second basic 2×2 FTM 100. The arrangement 500 alsoincludes first and second main amplifiers 524, 528 and a stand-byamplifier 526.

When the first and second main amplifiers 524, 528 are operative, thefirst split output 530 is coupled to the first split input 538 through afirst controllable switch 514, the first main amplifier 524, and asecond controllable switch 514. All the controllable switches of thearrangement 500 preferably comprise conventional RF relays having asingle-pole, double-throw (SPDT) contact arrangement, and are preferablyoperated by the controller 602 (FIG. 6). The second split output 532 andthe second split input 540 are each coupled to an open circuit throughthird and fourth controllable switches 516. Similarly, the fourth splitoutput 536 is coupled to the fourth split input 544 through a fifthcontrollable switch 522, the second main amplifier 528, and a sixthcontrollable switch 522. The third split output 534 and the third splitinput 542 are each coupled to an open circuit through seventh and eighthcontrollable switches 520. Ninth and tenth controllable switches 518couple the stand-by amplifier 526 to one of two paths, as needed.

When a failure of one of the first and second main amplifiers 524, 528is detected by the controller 602 through well-known monitoring andalarm techniques, the controller 602 is arranged and programmed toremove the failed amplifier from the network and to couple the stand-byamplifier 526 between the previously-unused split output and split inputof the affected splitter and combiner 300. For example, when a failureis detected in the second main amplifier 528, the controller 602operates the fifth and sixth controllable switches 522 to remove thesecond main amplifier 528 from the network and to terminate the fourthsplit output 536 and the fourth split input 544 with open circuits. Inaddition, the controller 602 operates the seventh, eighth, ninth, andtenth controllable switches 518 and 520 to couple the stand-by amplifier526 to the third split output 534 and to the third split input 542.

The amplifier switching arrangement 500 thus advantageously can handle afailure of one of the main amplifiers 524, 528 quickly and with nodegradation of insertion loss and no decrease in isolation between thesignals being amplified. One of ordinary skill in the art willappreciate that the amplifier switching arrangement 500 easily can beincreased to handle larger amplifier networks, such as the exemplary 4×4FTM amplifier network 400, and/or additional stand-by amplifiers.

Referring to FIG. 6, an electrical block diagram of an exemplaryfault-tolerant transmitter 600 in accordance with the present inventioncomprises the controller 602 for controlling the fault-toleranttransmitter. The fault-tolerant transmitter 600 further comprises afault-tolerant amplifier system 608, including, for example, the 4×4 FTMamplifier network 400 and a switching arrangement similar in principleto the amplifier switching arrangement 500, sized to handle the 4×4 FTMamplifier network 400. The fault-tolerant amplifier system 608 iscoupled to the controller 602 for control of the switching arrangementin the fault-tolerant amplifier system 608. The fault-toleranttransmitter 600 also includes a multi-carrier generator 604 coupled tothe controller 602 for generating a plurality of carrier signalsresponsive to communication traffic handled by the transmitter 600.Outputs of the multi-carrier generator 604 are coupled to thefault-tolerant amplifier system 608, whose own outputs preferably arecoupled to a plurality of RF antennas 606.

Referring to FIG. 7, a flow diagram 700 depicting a method forfacilitating fault tolerance in an RF amplifier system begins at step702 with feeding N input signals to a first Fourier Transform Matrix(FTM) to produce N intermediate signals, wherein N is a first integergreater than one. The flow diagram 700 next includes splitting 704 eachof the N intermediate signals via a non-isolating splitter to produce Msplit signals from each of the N intermediate signals, wherein M is asecond integer greater than one. At least one of the M split signalsfrom each of the N intermediate signals is then amplified 706 to produceat least N amplified signals. The at least N amplified signals arecoupled 708 to N non-isolating combiners, each having at least M inputports, to produce N combiner output signals. The N combiner outputsignals are applied 710 to a second FTM to produce N final outputsignals.

Thus, it should be clear from the preceding disclosure that the presentinvention provides a method and apparatus for facilitating faulttolerance in a radio frequency amplifier system. The method andapparatus advantageously will tolerate a failure in one of a pluralityof amplified paths with minimal degradation of insertion loss andwithout producing a substantial reduction in isolation between the RFsignals being amplified.

This disclosure is intended to explain how to fashion and use variousembodiments in accordance with the invention rather than to limit thetrue, intended, and fair scope and spirit thereof. The foregoingdescription is not intended to be exhaustive or to limit the inventionto the precise form disclosed. Modifications or variations are possiblein light of the above teachings. The embodiments were chosen anddescribed to provide the best illustration of the principles of theinvention and its practical application, and to enable one of ordinaryskill in the art to utilize the invention in various embodiments andwith various modifications as are suited to the particular usecontemplated. All such modifications and variations are within the scopeof the invention as determined by the appended claims, as may be amendedduring the pendency of this application for patent, and all equivalentsthereof, when interpreted in accordance with the breadth to which theyare fairly, legally, and equitably entitled.

1. A method for facilitating fault tolerance in a radio frequency (RF)amplifier system, the method comprising: feeding N input signals to afirst Fourier Transform Matrix (FTM) to produce N intermediate signals,wherein N is a first integer greater than one; splitting each of the Nintermediate signals via a non-isolating splitter to produce M splitsignals from each of the N intermediate signals, wherein M is a secondinteger greater than one; amplifying at least one of the M split signalsfrom each of the N intermediate signals to produce at least N amplifiedsignals; coupling the at least N amplified signals to N non-isolatingcombiners, each having at least M input ports, to produce N combineroutput signals; and applying the N combiner output signals to a secondFTM to produce N final output signals.
 2. The method of claim 1, whereinthe amplifying comprises amplifying all the M split signals to produce Mamplified signals corresponding to each of the N intermediate signals.3. The method of claim 2, wherein the coupling comprises coupling eachof the M amplified signals to a corresponding one of the N non-isolatingcombiners to produce the N combiner output signals.
 4. The method ofclaim 1, wherein the amplifying comprises: amplifying all the M splitsignals corresponding to each of the N intermediate signals, whentraffic through the RF amplifier system is above a predeterminedthreshold; and amplifying at least one of the M split signalscorresponding to each of the N intermediate signals, when trafficthrough the RF amplifier system is below the predetermined threshold. 5.The method of claim 4, further comprising, when amplifying the at leastone of the M split signals corresponding to each of the N intermediatesignals, and in response to detecting a failed amplifier, the uncouplingthe failed amplifier and coupling a stand-by amplifier to one of the Msplit signals not amplified prior to detecting the failed amplifier. 6.The method of claim 5, further comprising adding phasing lines to thenon-isolating splitter and to the non-isolating combiners, such that anopen circuit is reflected back to a tee thereof when the failedamplifier is uncoupled.
 7. An apparatus for facilitating fault tolerancein a radio frequency (RF) amplifier system, the apparatus comprising: afirst Fourier Transform Matrix (FTM) for receiving N input signals toproduce N intermediate signals, wherein N is a first integer greaterthan one; N non-isolating splitters coupled to the first FTM forsplitting each of the N intermediate signals to produce M split signalsfrom each of the N intermediate signals, wherein M is a second integergreater than one; a plurality of amplifiers coupled to the Nnon-isolating splitters for amplifying at least one of the M splitsignals from each of the N intermediate signals to produce at least Namplified signals; N non-isolating combiners coupled to the plurality ofamplifiers, each of the N non-isolating combiners having at least Minput ports, for producing N combiner output signals from the at least Namplified signals; and a second FTM for producing N final output signalsfrom the N combiner output signals.
 8. The apparatus of claim 7, whereinthe plurality of amplifiers include M×N amplifiers for amplifying allthe M split signals to produce M amplified signals corresponding to eachof the N intermediate signals.
 9. The apparatus of claim 8, wherein theapparatus is arranged such that each of the M amplified signals iscoupled to one of the M input ports of a corresponding one of the Nnon-isolating combiners to produce the N combiner output signals. 10.The apparatus of claim 7, further comprising: a controller formonitoring traffic through the RF amplifier system; and a plurality ofcontrollable RF switches coupled to the controller and coupled to theplurality of amplifiers, wherein the controller and the plurality ofcontrollable RF switches are arranged and programmed such that: theplurality of amplifiers amplify all the M split signals corresponding toeach of the N intermediate signals, when traffic through the RFamplifier system is above a predetermined threshold; and the pluralityof amplifiers amplify at least one of the M split signals correspondingto each of the N intermediate signals, when traffic through the RFamplifier system is below the predetermined threshold.
 11. The apparatusof claim 10, further comprising a stand-by amplifier coupled to theplurality of controllable RF switches, and wherein the controller andthe plurality of controllable RF switches are further arranged andprogrammed such that, when amplifying the at least one of the M splitsignals corresponding to each of the N intermediate signals, and inresponse to detecting a failed one of the plurality of amplifiers, thefailed one of the plurality of amplifiers is uncoupled from acorresponding one of the M split signals, and the stand-by amplifier iscoupled to a corresponding one of the M split signals not amplifiedprior to detecting the failed one of the plurality of amplifiers. 12.The apparatus of claim 11, wherein the N non-isolating splitters and theN non-isolating combiners each comprise a tee; and a phasing linecoupled to the tee, the phasing line arranged such that an open circuitis reflected back to the tee when the failed one of the plurality ofamplifiers is uncoupled.
 13. A fault-tolerant transmitter, comprising: acontroller for controlling the fault-tolerant transmitter; amulti-carrier generator coupled to the controller for generating N inputsignals comprising a plurality of radio frequency (RF) carriers; a firstFourier Transform Matrix (FTM) coupled to the multi-carrier generatorfor receiving the N input signals to produce N intermediate signals,wherein N is a first integer greater than one; N non-isolating splitterscoupled to the first FTM for splitting each of the N intermediatesignals to produce M split signals from each of the N intermediatesignals, wherein M is a second integer greater than one; a plurality ofamplifiers coupled to the N non-isolating splitters for amplifying atleast one of the M split signals from each of the N intermediate signalsto produce at least N amplified signals; N non-isolating combinerscoupled to the plurality of amplifiers, each of the N non-isolatingcombiners having at least M input ports, for producing N combiner outputsignals from the at least N amplified signals; and a second FTM forproducing N final output signals from the N combiner output signals. 14.The fault-tolerant transmitter of claim 13, wherein the plurality ofamplifiers include M×N amplifiers for amplifying all the M split signalsto produce M amplified signals corresponding to each of the Nintermediate signals.
 15. The fault-tolerant transmitter of claim 14,wherein the fault-tolerant transmitter is arranged such that each of theM amplified signals is coupled to one of the M input ports of acorresponding one of the N non-isolating combiners to produce the Ncombiner output signals.
 16. The fault-tolerant transmitter of claim 13,further comprising: a plurality of controllable RF switches coupled tothe controller and coupled to the plurality of amplifiers, wherein thecontroller and the plurality of controllable RF switches are arrangedand programmed such that: the plurality of amplifiers amplify all the Msplit signals corresponding to each of the N intermediate signals, whentraffic through the RF amplifier system is above a predeterminedthreshold; and the plurality of amplifiers amplify at least one of the Msplit signals corresponding to each of the N intermediate signals, whentraffic through the RF amplifier system is below the predeterminedthreshold.
 17. The fault-tolerant transmitter of claim 16, furthercomprising a stand-by amplifier coupled to the plurality of controllableRF switches, and wherein the controller and the plurality ofcontrollable RF switches are further arranged and programmed such that,when amplifying the at least one of the M split signals corresponding toeach of the N intermediate signals, and in response to detecting afailed one of the plurality of amplifiers, the failed one of theplurality of amplifiers is uncoupled from a corresponding one of the Msplit signals, and the stand-by amplifier is coupled to a correspondingone of the M split signals not amplified prior to detecting the failedone of the plurality of amplifiers.
 18. The fault-tolerant transmitterof claim 17, wherein the N non-isolating splitters and the Nnon-isolating combiners each comprise a tee; and a phasing line coupledto the tee, the phasing line arranged such that an open circuit isreflected back to the tee when the failed one of the plurality ofamplifiers is uncoupled.